Question: Vanessa is 4 times as old as Tiffany and is also 21 years older than Tiffany. How old is Tiffany?
Answer: We can use the given information to write down two equations that describe the ages of Vanessa and Tiffany. Let Vanessa's current age be $v$ and Tiffany's current age be $t$ $v = 4t$ $v = t + 21$ Now we have two independent equations, and we can solve for our two unknowns. Since we are looking for $t$ , and both of our equations have $v$ alone on one side, this is a convenient time to use elimination. Subtracting the second equation from the first equation, we get: $0 =$ $4t$ $-$ $ (t + 21)$ which combines the information about $t$ from both of our original equations. Solving for $t$ , we get: $3 t = 21$ $t = 7$.